As someone born in 1995, I don't have any real emotional connection to the Challenger explosion. It's pretty bizarre to think that children born after the 9/11 attacks will probably feel the same indifference.
[0]http://freakonomics.com/2015/05/20/failure-is-your-friend-a-...
For me the "ah hah" moment was when it hit me that "Where were you when you heard about Challenger?" was my generation's version of, "Where were you when JFK was assassinated?"
Another easily observed one is music. Very few people are aware of much that happened in popular music after they hit 25.
You can listen through 65 years of pop music made so far. Then, if you live 80 years, you only lose about 45,8% of all pop-music you could have heard during your lifetime. That's not half bad.
If you include some blues, jazz and classical, that percentage goes down significantly.
Regards, 29 year old with 4 year long amnesia about music.